Method and apparatus for searching a plurality of destination numbers

ABSTRACT

A method and apparatus for improving call connection to one of a plurality of destination numbers on a calling list is disclosed. The method involves monitoring the inband signals between an interrogating mobile switching center and a remote node during call setup procedures. An inband monitoring device looks for terminating signals indicating that call setup to the remote nodes will not be completed. Upon detection of such a termination signal, the call setup procedure is immediately discontinued without waiting for expiration of a call answer timeout period.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present relates to caller destination lists, and more particularly,to a method for searching through a plurality of destination numbersassociated with a single calling list by monitoring inband callingsignals.

2. Description of Related Art

Calling services exist that enable an individual to call a subscriberthrough a particular location number that enables the call tosequentially cycle through a number of locations at which the subscribermay be located. Once the initial call is made, a number of sequentialcalls are subsequently initiated to a list of potential destinationnumbers where the subscriber may be located.

When calls are routed to a destination number, the switch controllingthe call must determine that the call cannot be completed before goingto the next destination number on the calling list. In situations wherethe call is delivered over trunks providing call failure information(such as ISUP), the switch may use the call failure information todisconnect the call and go to the next destination number on the list.

However, when calls are routed through trunks that provide call failureinformation inband, there is a potential for the call to be incorrectlyconnected to a failure announcement or call setup can be delayed whilewaiting for a call answer timeout period to expire. A method enabling abetter utilization of system information to speed up the process formoving through the list of destination numbers would greatly benefitcallers and conserve system resources.

SUMMARY OF THE INVENTION

The present invention describes a method and apparatus for improvingcall connection to one of a plurality of destination numbers on acalling list. A call is initiated from an interrogating mobile switchingcenter in an attempt to contact a third party within either a mobilenetwork or external public telephone network. Initiation of the outboundcall to one of the destination numbers causes an inband monitoringdevice to begin monitoring the inband signals received over a trunkline.

While monitoring, the device looks for inband signals indicating that acall setup cannot be completed with the destination number. Such signalswould include the tones associated with a busy signal, a call congestionsignal, or special information tones. When these types of tones aredetected within the inband signal, call setup procedures are immediatelyaborted with the present destination number so that the search mayproceed to the next destination number on the calling list.

In this manner, call setup may be discontinued without causing eitherimproper connection to the playback of a call termination recording ordelaying processing of the next destination number during a call answertimeout period.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference ismade to the following detailed description taken in conjunction with theaccompanying drawings wherein:

FIG. 1 is a block diagram of a communications network including a devicefor monitoring inband signals at an interrogating mobile switchingcenter; and

FIG. 2 is a flow diagram illustrating the method by which the inbandsignal monitoring device searches for signals potentially terminatingthe call setup procedure.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there isillustrated a communication system including a device for monitoringinband signals. An outside caller accesses the system 10 through aninterrogating mobile switching center (MSC) 15. The interrogating mobileswitching center 15 contacts the home location register 20 of thesubscriber who is trying to be contacted. When the subscriber's serviceprofile includes the searching feature, the HLR provides from a callinglist 25 a first destination number 30 at which to attempt contact withthe subscriber and calculates a position value 35 indicating theposition in the calling list of the next destination number. Thedestination number 30 and position value 35 are transmitted to theinterrogating MSC 15 for further processing.

The interrogating MSC 15 uses the destination number 30 to initiate acall setup procedure to the first potential subscriber location. Thiscall may be setup through a mobile network to an MSC/VLR 40 in anattempt to contact a mobile station 45, or may contact a telephonewithin a public switched telephone network 50 through a gateway mobileswitching center 55.

In a normal situation a call can fail connection in one of two methods.The interrogating MSC 15 may quickly determine failure of the call setupfrom received call process signals. For example, an ISUP RELEASE messageor a signaling error from a node may indicate call setup failure.However, if the interrogating MSC 15 cannot determine the existence of acall setup failure from received call process signals, it must wait fora timeout period for an expected answer signal to expire before the callmay be disconnected. Thus, if the call was receiving a busy tone, acongestion tone or special information tones, an inquiring MSC 15 wouldstill wait for the expiration of the timeout period even though inbandsignals indicated the call cannot be completed.

The busy tone, congestion tone and special information tones aretransmitted to the interrogating MSC 15 as an inband signal. The inbandsignal monitoring device 60 monitors the inband signals received from aremote node over a trunk line to determine if signals indicating a callconnection cannot be completed are present. Inband signals compriseacoustic signals sent toward the calling subscriber within the voicechannel associated with the call. Immediately upon detection andrecognition of a busy tone, congestion tone, or special informationtone, a call setup procedure is discontinued without waiting forexpiration of an answer timeout period. This saves time and conservessystem resources that would otherwise be tied up in a call that cannotbe completed. It should of course be realized that the three types oftones discussed above are not the only ones which may be monitored forby the inband signal monitoring device 60, but any other type of signalor tone transmitted as an inband signal may be monitored to moreefficiently process the calling list 25.

The inband monitoring device 60 may seize control of a trunk line andbegin monitoring inband signals in a variety of manners. The device 60may gain control in response to a command from the HLR 20 based uponsubscriber information stored within HLR. The interrogating MSC 15 mayautomatically connect the monitoring device 60 based upon the routing ofthe outgoing call to a remote node. Finally, the interrogating MSC 15may connect the device based upon reception of a backwards signalindicating interworking between the interrogating MSC 15 and a remotenode. The monitoring device 60 would be blind to particular types ofbackward tones, such as ringing tones, that do not indicate a callcannot be connected.

Referring now to FIG. 2, there is illustrated a flow chart describingthe manner in which the inband monitoring device 60 works in conjunctionwith the interrogating mobile switching center 15. After a call isinitiated at step 75, the inband monitoring device 60 is connected atstep 80 to monitor inband signals on a connected trunk line. The inbandmonitoring device 60 searches for tones or signals indicating that thecall setup to the remote node will not be completed.

Inquiry step 85 determines if a busy tone has been detected. If no busytone is detected, inquiry step 90 checks for a congestion tone. If nocongestion tone is detected, inquiry step 95 monitors for specialinformation tones. If any of the inquiry steps 85-95 receive anaffirmative response, the call is disconnected at step 100 and controlpasses to the next destination number at step 102. Otherwise, no calldisconnection tones are detected and call processing continues at step105 wherein the call will either be connected due to an answer by thesubscriber, or expiration of a timeout period causes processing to passto the next destination number at step 102.

Although a preferred embodiment of the method and apparatus of thepresent invention has been illustrated in the accompanying Drawings anddescribed in the foregoing Detailed Description, it is understood thatthe invention is not limited to the embodiment disclosed, but is capableof numerous rearrangements, modifications, and substitutions withoutdeparting from the spirit of the invention as set forth and defined bythe following claims.

What is claimed is:
 1. A method for improving call connection to acalling list, comprising the steps of:initiating a call to one of aplurality of destination numbers on a calling list; monitoring inbandsignals during call setup for an inband signal indicating call setupcannot be completed; and aborting the call setup if the inband signalindicates the call setup cannot be completed.
 2. The method of claim 1wherein the step of monitoring comprises the step of monitoring theinband signal during call setup for a busy tone.
 3. The method of claim2 wherein the step of aborting the call setup comprises the step ofaborting the call setup if the busy tone is detected.
 4. The method ofclaim 1 wherein the step of monitoring comprises the step of monitoringthe inband signal during call setup for a congestion tone.
 5. The methodof claim 4 wherein the step of aborting the call setup comprises thestep of aborting the call setup if the congestion tone is detected. 6.The method of claim 1 wherein the step of monitoring comprises the stepof monitoring the inband signal during call setup for specialinformation tones.
 7. The method of claim 6 wherein the step of abortingthe call setup comprises the step of aborting the call setup if thespecial information tones are detected.
 8. The method of claim 1 whereinthe step of monitoring comprises the step of monitoring the inbandsignal during call setup for any one of a busy tone, a congestion tone,or special information tones.
 9. The method of claim 8 wherein the stepof aborting the call setup comprises the step of aborting the call setupif the inband signal includes at least one of the busy tone, thecongestion tone or the special information tones.
 10. The method ofclaim 1 further including the step actuating an inband signal monitoringdevice in response to receipt of a backward signal indicatinginterworking during call initiation.
 11. The method of claim 1 furtherincluding the step actuating an inband signal monitoring device inresponse to a routing request during call initiation.
 12. The method ofclaim 1 further including the step of actuating an inband signalmonitoring device in response to a command from an HLR providing theplurality of destination numbers.
 13. The method of claim 1 wherein thestep of aborting the call setup occurs prior to a call answer timeoutperiod.
 14. A method for improving call connection to one of a pluralityof destination numbers on a calling list, comprising the stepsof:actuating an inband signal monitoring device in response to anattempted call setup with one of the plurality of destination numbers;monitoring inband signals during call setup for tones indicating a busysignal, a congestion signal, and a special information signal; andaborting the call setup if any one of the busy signal, congestion signaland special information signal are detected prior to termination of thecall setup due to a call answer timeout period.
 15. The method of claim14 wherein the step of actuating the inband signal monitoring deviceoccurs in response to receipt of a backward indicating interworkingsignal during call initiation.
 16. The method of claim 14 wherein thestep of actuating the inband signal monitoring device occurs in responseto a routing command during call initiation.
 17. The method of claim 14wherein the step of actuating the inband signal monitoring device occursin response to a command from an HLR providing the plurality ofdestination numbers.
 18. A system for improving call connection to oneof a plurality of destination numbers on a calling list, comprising:aswitching center for initiating a call setup to the one of the pluralityof destination number on the calling list; and means for monitoring aninband signal to the switching center during call setup for atermination signal indicating call setup cannot be completed andterminating the call setup upon detection of the terminating signal, themeans for monitoring responsive to initiation of call setup by theswitching center.
 19. The system of claim 18 wherein the terminatingsignal comprises busy tones.
 20. The system of claim 18 wherein theterminating signal comprises congestion tones.
 21. The system of claim18 wherein the terminating signal comprises special information tones.22. The system of claim 18 wherein the means for monitoring terminatescall setup prior to a call answer timeout period if a termination signalis detected.